suddenly my Windows desktop - along with all programs - turned black and white. Pressing Ctrl+Alt+Del still brings up the *blue* screen (lock, change password, start task manager, ...), and after rebooting, Windows' log-in screen is as colorful than ever, so I'm really puzzled... I can't say for sure that I didn't accidentally hit some mysterious keyboard shortcut, but I wouldn't know which one.

I *really* hope someone has an idea regarding how to fix this. The only solution I could find with Google was to update the gfx card driver (Intel HD Graphics 520). It didn't make sense to me but I tried it anyway. Since I already had the latest version I downloaded and installed an older one, but that didn't help.